My source in government says:
For art work, they need to see if it's in the collections of any museums and get permissions from the museums registrars office. I'd avoid anything that's not in collections because then you have to mess with estates and stuff. If they're talking about contemporary living artists, they may be able to approach the artist or their gallery also. For example, to use a Chuck Close, I would go through Pace in NY. Since they're looking for digital rights, it may be tricky as there are issues of downloading and perpetuity and stuff. But since this is for school, maybe they'll catch a break.
Also, check out:
Once you read all about the issue, and then have a lis of artists/artwors you are considering using, then maybe call Volunteer Lawyers for the Arts to discuss your plan. Make sure they know its a school project.